1. Field of the Invention
The present invention relates to a gear device.
2. Description of the Related Art
Heretofore, there has been known a gear device designed to obtain an output rotation at a speed reduced from an input rotation by allowing an external gear to be rockingly rotated while being meshed with internal teeth of an outer cylinder, according to an eccentric portion of a crankshaft. One example of this type of gear device is disclosed in the JP 2002-106650.
FIG. 5 is a vertical sectional view of a gear device disclosed in the JP 2002-106650. In this gear device, a crankshaft 104 having two eccentric portions 104a, 104b arranged in side-by-side relation in an axial direction thereof is provided inside an outer cylinder 102 in a rotatable manner about an axis thereof. Although not illustrated in FIG. 5, a similar crankshaft other than the crankshaft 104 is also provided inside the outer cylinder 102, and these crankshafts are arranged at even intervals around a central axis of the outer cylinder 102. External gears 108a, 108b are mounted to the eccentric portions 104a, 104b of each of the crankshaft 104 and other crankshaft, through bearings 106a, 106b, respectively. A large number of internal-tooth pins 102a are provided on an inner surface of the outer cylinder 102 over the entire circumference thereof. Each of the external gears 108a, 108b is meshed with the internal-tooth pins 102a. 
Further, a carrier 112 is housed in the outer cylinder 102. This carrier 112 is mounted to the outer cylinder 102 through a pair of bearings 110a, 110b in a relatively and coaxially rotatable manner with respect to the outer cylinder 102. The outer cylinder 102 is joined to a partition member 114 in one of axially opposite end portions thereof. On the other hand, the carrier 112 is joined to a table 116 as a turning body, at an end portion thereof on the side opposite to the partition member 114. Each of the carrier 112, the partition member 114, the table 116 and the external gears 108a, 108b has a through-hole provided in a central region thereof to axially penetrate therethrough.
A cylindrical body 118 is inserted in the through-holes, and fixed to the carrier 112. Specifically, the cylindrical body 118 has a flange 118a provided on an outer surface thereof at a position adjacent to a lower end portion thereof to protrude radially outwardly. This flange 118a is fastened to the carrier 112 by a plurality of bolts 120, whereby the cylindrical body 118 is fixed to the carrier 112. The lower end portion of the cylindrical body 118 protrudes from a lower end of the carrier 112. In assembling between the table 116 and the carrier 112, the lower end portion of the cylindrical body 118 protruding from the lower end of the carrier 112 is fitted into the through-hole of the table 116. This allows central axes of the table 116 and the carrier 112 to be readily aligned each other. Further, a ring-shaped external-fitting member 115 is mounted around the through-hole opened in an upper end surface of the partition member 114. An upper end portion of the cylindrical body 118 is inserted in the external-fitting member 115, while protruding from an upper end of the partition member 114 through the through-hole of the partition member 114. A sealing member 115a is provided between an inner surface of the external-fitting member 115 and the outer surface of the cylindrical body 118. The sealing member 115a is operable to prevent lubricant filled in the gear device from leaking from between the inner surface of the external-fitting member 115 and the outer surface of the upper end portion of the cylindrical body 118.
However, in the gear device disclosed in JP 2002-106650, the cylindrical body 118 is fixed to the carrier 112 only by a structure where the flange 118a provided adjacent to the lower end portion of the cylindrical body 118 is fastened to the carrier 112. Consequently, when the cylindrical body 118 is rotated together with the carrier 112, vibration occurs in the upper end portion of the cylindrical body 118 in a radial direction thereof, and thereby a small gap is likely to occur between the upper end portion of the cylindrical body 118 and the sealing member 115a to cause leakage of lubricating oil.
Further, in the gear device disclosed in JP 2002-106650, the flange 118a is integrally provided on the cylindrical body 118 to protrude outwardly in the radial direction of the cylindrical body 118. As a prerequisite to accurately form the flange 118a, it is necessary to form the flange 118a by cutting. In this case, it is necessary to entirely remove axially opposite sides of the flange 118a in a material of the cylindrical body 118, by cutting. Therefore, most of the cylindrical body 118 has to be subjected to cutting in a length direction thereof, resulting in an increase of time and effort required for the machining of the cylindrical body.